LOL! Get kickbacks from GK? Even as much into Ampegs as I am, I'd never say that about Ampeg to a kid trying to choose gear!If you want to buy today, go with the GK set. You have already played through one, albeit a different cab, and loved it. I'll bet this one will sound similar to what you liked. The Ampeg is completely unknown to you and despite some people going gaga over anything they make, many of us cannot dial-in a tone we like with an Ampeg. The GK MB500 head is great and more compact and lighter than the Ampeg (which is pretty big and heavy for a Class D amp). The MB500 also comes with a footswitch which allows you a second channel on the amp which is cool for soloing or mood changes in a song.
Order from Musician's Friend today and they'll give you 15% off (only if you call, not online).
Decision made. Go order.
Instead, I'd say go to GC and try out whatever they have there. If you can't find them (and it's possible, especially with the PF410hlf being new), then try what they have and see what you think. GK and Ampeg are both very well-respected brands who make classic gear. I prefer Ampeg, someone else might not. All of it is immaterial to you, the kid putting his money on the line, and all that matters is what YOU like.